Linear motors are used in a variety of electrical devices. For example, photolithography systems and other semiconductor processing equipment utlize linear motors to precisely position a reticle stage holding a reticle and a wafer stage holding a wafer. Alternately, linear motors are used in other devices, including elevators, machine tools, metal cutting machines, and inspection machines.
A typical brushless electric motor includes a magnet component and a conductor component The magnet component includes a plurality of permanent magnets positioned side-by-side. Each of the magnets generates a surrounding magnetic field. The conductor component includes one or more coils. When electric current flows in the coils, a Lorentz type force is created in a direction mutually perpendicular to the direction of the current in the coils and the magnetic field of the magnets. The force can be used to move one of the components relative to the other component of the motor.
A typical brushless linear electric motor generates stray magnetic fields external to the motor. Unfortunately, the stray magnetic fields can influence a number of manufacturing, measurement and/or inspection processes. For example, electron beams are influenced by AC magnetic fields of sufficient magnitude. As a result thereof, the AC linear electric motors must be positioned a relatively large distance away from the electron beam, typically outside a system magnetic shield. More specifically, for an electron beam projection lithography system, the linear motors used to position the reticle stage and the wafer stage must be positioned a relatively large distance away from the electron beam. Similar design considerations apply to other charged particle lithography systems, including both electron and ion beam systems, as well as charged particle inspection or metrology systems.
In order to increase the performance of electron beam lithography systems, it is necessary to integrate the electric motors directly into the reticle stage and the wafer stage. This means the motors must be positioned within the magnetic shield and close to the electron beam. As a result thereof, the stray AC magnetic fields from the motors present a problem.
One attempt to solve this problem includes adding one or more additional magnetic shields that block the stray AC magnetic fields from the motor. Unfortunately, the magnetic shields will require a sizable opening to allow for movement of the moving part of the motor. Further, the magnetic shields can increase the required size of the stage and the motor. This increases the size and weight of the entire machine.
In light of the above, there is a need for a conductor component and an electric motor that has reduced stray magnetic fields, without significantly influencing the dynamic performance of the motor. Further, there is a need for a brushless electric motor for an exposure apparatus that utilizes a charged particle beam. Moreover, there is a need for an improved motor for precisely positioning a device during a manufacturing, measurement and/or an inspection process. Additionally, there is a need for an exposure apparatus capable of manufacturing precision devices, such as high density, semiconductor wafers.